1. Field of the Invention
This invention relates generally to the correction of digital signals and, more specifically, is directed to the correction of errors in digital audio signals which are, for example, recorded on a magnetic tape or the like.
2. Description of the Prior Art
It is known to use the so-called cross-interleave technique for transforming a digital data signal into an error correctable code structure for digital data transmission or for recording and reproducing. It is the usual practice, when using the cross-interleave technique, to use modulo-2 adders to generate two parity series P and Q, each representing predetermined numbers of the data words in two different arrangements. Because each word of the digital data signal will be contained in the two parity series, this known cross-interleave technique provides a substantial error correcting capability, particularly when the correcting processes are repeatedly performed.
In the error correcting system employing the cross-interleave technique in a conventional PCM tape recorder, for example, a so-called 8 mm VTR for digital audio signals, if only one error word is found to exist in the P or Q series by detecting word error pointers of such series, that single error word is corrected. However, in all other cases, that is, when no error word exists so that it is unnecessary to correct the same, or when two or more error words exist and hence cannot be corrected, the word error pointers are merely read out and no error correction process is performed. Thus, when no error word exists or when two or more error words exist, the time required to read out the word error pointers is wasted.
When using the cross-interleave technique, the number of error words that can be corrected is increased, so that the error correcting capability is improved, by increasing the number of times that the error correcting processes are repeated in respect to the P and Q series. However, since the overall time available for the error correcting processes is usually limited to a predetermined time interval, the previously described wasted time required for reading out word error pointers when no error correction is or can be effected, necessarily limits the number of repetitions of the correcting processes that can be performed within such limited time interval. Hence, enhancement of the correcting capability is restricted.